In general, a lithography technique used to manufacture a semiconductor device includes a masking process and an exposure process. That is, the lithography technique includes steps for preparing a photomask on which a pattern is recorded by using a high precision optical system and transferring the pattern on the photomask to a silicon wafer by-using the exposure process.
Such lithography technique is an essential technique for obtaining a mask pattern in a semiconductor device manufacturing process. As the integration degree of the semiconductor device becomes higher, the line width of the mask pattern formed on the silicon wafer becomes narrower. The resolution corresponding to the line width implemented with an optical system is represented by the following Equation 1.Resolution=k1·λ/(NA)  [Equation 1]
In Equation 1, k1 is a lithography process variable, λ is a wavelength of a light source, and NA is a numerical aperture of an optical system.
Since the line width of a pattern becomes narrower as the resolution of the optical system is higher, many approaches for improving the resolution have been developed. As shown in Equation 1, the resolution can be improved by reducing the process variable k1, increasing the numerical aperture NA, or using a short-wavelength light source.
In the current lithography technique used in a semiconductor device manufacturing process, the process variable k1 can be reduced down to 0.4˜0.3, and the numerical aperture NA of about 0.8 can be obtained by an optical system. Under these conditions, when a krypton fluoride (KrF) excimer laser having a wavelength of 248 nm is used as a light source, the resolution determining the line width in the lithography is in a range of 90 to 120 nm.
When an argon fluoride (AgF) laser having a wavelength of 193 nm would be used as a light source, the resolution determining the line width in the lithography will be improved to a range of 70 to 100 nm.
However, in order to improve the resolution by using the ultraviolet light source having a shorter wavelength, a highly-qualified fused silica used as an optical member of a conventional high precision optical system must be replaced with calcium fluoride (CaF) and a photoresist sensitive to the ultraviolet light must be used. In addition, if an exposure process is performed by using a mask pattern, light is refracted at an aperture, so that the result of the exposure process may be deteriorated.
When light passes through a hole having a diameter of several nanometers which is relatively small in compare with the wavelength of the light, the intensity of light transmitting the hole is proportional to the fourth power of the diameter of hole. Therefore, as the diameter of the aperture is reduced, the intensity of light is rapidly decreased in inverse proportion to the fourth power of the diameter of aperture. Therefore, when the diameter of the aperture through which the light source passes is reduced to form a nano pattern (hereinafter, sometimes referred to as “fine pattern”), the intensity of the light is reduced, so that the time period for the exposure process and the scanning process to form the nano pattern are lengthened.
In consideration of the developing speed in the integration degree of semiconductor devices, the resolution of the lithography technique is expected to reach about 55 nm in a few years. Lithography techniques using an ultraviolet light or electron beams are actively researched and developed, but these techniques still remains at a laboratory level. For the last decade, the lithography technique has imposed limitation on the integration degree of semiconductor devices. Therefore, a novel fine patterning technique is urgently demanded.
An object of the present invention is, therefore, to overcome a technical limitation on the resolution by providing a novel fine patterning technique of directly recording a fine pattern on a photoresist without using a photomask.
Another object of the present invention is to provide an apparatus using a laser source suitable for a sensitive wavelength of conventional photoresists.
In order to achieve the aforementioned objects, a two-dimensional light-modulating fine aperture array apparatus utilizes two well-known approaches for transmitting a large amount of light through apertures having a size of tens of nanometers. The first approach is disclosed in an article by X. Shi and L. Hesselink, titled “Mechanism for enhancing power throughput from planar nano-apertures for near-field optical data storage” in Japan Journal of Applied Physics Vol. 41, pp. 1632-1635 (2002). According to the first approach, the transmittance can be greatly improved by using a metal optical waveguide aperture.
The second approach is disclosed in an article by Y. J. Kim, K. S. Suzuki, and K. Goto, titled “Parallel recording array head of nano-aperture flat-tip probes for high-density near-field optical data storage” in Japan Journal of Applied Physics. Vol. 40, pp 1783-1789 (2001) and another article by K. Goto, Y. J. Kim, S. Mitsugi, K. Suzuki, K. Kurihara and T. Horibe, titled “Micro-optical two-dimensional devices for the optical memory head of an ultrahigh data transfer rate and density system using a vertical cavity surface emitting laser array” in Japan Journal of Applied Physics. Vol. 41, pp. 4835-4840 (2002). According to the second approach, focal point size of a light can be greatly reduced by coupling a lens having a large numerical aperture NA with a medium having a high index of refraction.